running and ground water
IV. RUNNING WATER and GROUNDWATER
A) The Hydrologic Cycle
Runoff: Occurs when the rate of rainfall is greater than the ground’s ability to absorb it.
Infiltration: Water that soaks into the ground.
Transpiration: Water that infiltrates into the ground, is absorbed by plants, and is released into the atmosphere by plants.
B) Running Water: Surface Water
Stream Flow: Factors that determine velocity (feet per second) of streams:
a) Gradient: Slope of a stream channel (Mississippi River 10 cm/km).
b) Channel characteristics:
i) Channel Size
ii) Channel Shape
iii) Channel Roughness
Larger, Straighter, Smoother channel is fastest
c) Discharge: Volume of water flowing past a point per unit time (cubic feet per second).
Changes from Upstream to Downstream:
a) Discharge increases toward the mouth of the stream (tributary streams add more water).
b) Velocity is greater at the mouth of the stream than at the headwaters (greater discharge, larger channel, smoother bed).
Base Level: The Lowest Point to Which a Stream Can Erode:
a) Ultimate Base Level: Sea Level—“the lowest level to which a stream could lower the land.”
b) Temporary or Local Base Level: Ledges of rock, lakes, or large streams—which act as base level for tributary streams.
4) The Work of Streams a) Erosion: Removal of rock and soil.
b) Transportation: Streams transport sediment in three ways:
i) Dissolved Load: Minerals dissolved in water.
ii) Suspended Load: Silt and fine sand carried in water.
iii) Bed Load: Large particles rolling along the bottom of the stream channel.
(iv) Definitions:
Stream Competence: Maximum particle size that a stream can transport.
Stream Capacity: Maximum sediment load that a stream can carry.
c) Deposition
i) As stream velocity decreases, sediment begins to drop out of water—largest particles first.
ii) Alluvium: The general term for stream-deposited sediments.
iii) Delta: When a stream enters still waters, sediments deposit in a triangular shape (also called Greek letter “delta”).
iv) Sorting: The process by which various particle sizes are separated, controlled by Stoke’s Law of Sedimentation:
Artificial Sorting in a beaker.
Natural Sorting in shorelines.
Natural Sorting in levees: When a stream overflows its banks, its water velocity drops immediately—which drops coarse sediment along the border of the stream channel.
v) Yazoo Tributary: Tributary streams which can’t climb over the natural levees, so they run parallel (alongside) the major stream or river.
5) Stream Valleys
a) Narrow Valleys: A stream that is actively down-cutting to reach base level. b) Wide Valleys: “Once a stream has reached base level, stream energy becomes directed side-to-side.”
(i) Floodplains: A flat valley floor produced by side-to-side cutting of a stream—process is both erosional and depositional:
Cut Bank.
Point Bar.
(ii) Meanders: Streams that flow on floodplains in sweeping bends.
6) Floods and Flood Control
a) Causes of Floods:
(i) High intensity rains.
(ii) Rapid melting of snow.
(iii) Human interference: Urbanization, pavement increases runoff.
b) Flood Control:
(i) Artificial Levees: Earthen mounds built on the banks of rivers to increase water volume.
Sediment builds up in channel, must be removed.
Sediment would normally spread over the flood plain.
(ii) Flood Control Dams: Store flood water, let it out slowly—problem:
Dams trap sediment, sediment doesn’t reach beaches, beaches erode.
(iii) Channelization: Change the channel (straighten it) to speed flow of water to prevent it from reaching flood levels.
(iv) Non-Structural Approaches: Flood Plain Management—minimize development on flood plains, promote more appropriate uses.
7) Drainage Basins: Land area that contributes water to a stream.
8) Drainage Patterns:
(a) Dendritic Drainage: Common on uniform sediments.
(b) Rectangular Drainage: Bedrock that is crisscrossed by joints or faults.
C) Groundwater: Water Beneath the Surface
Importance of Groundwater:
a) 14% of freshwater in the hydrosphere (ice is 85% of freshwater).
b) 94% of freshwater (when just considering liquid water—not ice).
c) 50% of water used by population in the United States is groundwater.
Distribution and Movement of Groundwater: a) Groundwater Definitions:
Zone of Saturation: Zone of sediment in which all the open spaces in the sediment are filled with water.
Water Table: Top of the zone of saturation—the shape of the water table is usually a subdued replica of the surface topography.
Zone of Aeration: Sediments above the water table, which are not saturated, also called the "Vadose Zone."
b) Movement of Groundwater:
i) Porosity: Percentage of the total volume of the rock that consists of pore spaces.
ii) Permeability: Ability to move water through connected pore spaces.
iii) Aquifer: Rocks and sediments which freely transmit water.
iv) Aquitard: Sediments or rock that are impermeable to water.
c) Water Wells:
i) Drawdown: The lowering of the water table as water is withdrawn from a well—Groundwater moves slowly, so as water comes out of the well, the water level in the aquifer lowers.
ii) Cone of Depression: The temporary removal of water from an aquifer, in the shape of a cone-shaped volume—replenished when the well is off.
iii) Artesian Wells: When groundwater rises in a well, above the level where it was first encountered—water that is pressured.
iv) Flowing Artesian Well: Water flows out of the well because well pressure reaches above ground surface—“J” tube example.
v) Non-flowing Artesian Well: Water rises in the well but does not flow—well pressure does not reach the ground surface.
3) Springs: Where the water table intersects the ground surface.
a) Hot Springs:
Spring water that is 10 to 15 degrees F higher than mean annual air temperature.
i) Average Geothermal Gradient (Tarbuck and Lutgens): 1 degree F per 100 feet depth.
ii) Hot springs form when surface water circulates to depth, becomes heated, finds an easy way to surface and rises.
Examples: Elsinore and Glen Ivy Hot Springs examples.
iii) Hot springs also form over cooling igneous rocks (e.g., Round Valley, CA).
b) Geysers: Intermittent hot springs that occur in hot igneous rock, that contain chambers (openings):
i) Water 1000 feet deep is under pressure—requires higher temperature to boil (450 degrees F).
ii) Heating causes water to expand.
iii) Expanding water flows out the spring—which decreases pressure at the bottom of the hole.
iv) Pressure release at bottom of hole allows water to boil (pressure cooker example).
v) Boiling produces steam, which makes the geyser erupt.
4) Environmental Problems Associated with Groundwater
a) Overproduction: Pumping exceeds recharge. b) Land Subsidence: Caused by groundwater withdrawal. - i) Soil strength = grain to grain strength (effective stress) + buoyant force (pore pressure). - ii) If water is withdrawn, pore pressure is reduced—effective stress is increased—starts subsidence. - iii) Increased effective stress shifts soil grains—subsidence continues. - iv) Next, clays are dewatered—which continues subsidence.
c) Groundwater Contamination: i) Common Sources of Pollution: - Domestic Sources: Septic tanks, broken sewers, polluted runoff (parking lots). - Agriculture: Fertilizers. - Mining: Untreated rainwater and groundwater. - Industry: Underground storage tanks (gasoline stations). - Old Landfills.
ii) Common Solutions: - Alternate use of polluted. - Surface Aeration. - “Dilution is the solution to pollution.”
D) Caverns
1. Formed at or below the zone of Saturation—dissolved by carbonic acid (dripping water contacts air, combines with CO₂). 2. Karst Topography: - Solution topography—formed by chemical dissolution of limestone rather than by physical erosion of streams. a) Sink Holes: Formed by collapsing ceiling of caverns—sinkholes only occur in limestone!!! b) Disappearing Streams: Stream that pours into a sinkhole. c) Rising Streams: Streams that bubble up from a sinkhole.